DL-phenylalanine is a precursor for neurochemicals and adrenal hormones such as dopamine, epinephrine, norepinephrine, adrenaline and noradrenaline, which are released during times of stress or excitement. The adrenal hormones produced can help the body prepare for action during times of fight or flight. The neurochemicals produced give rise to the feelings of euphoria, happiness and mood elevation.*D-phenylalanine is known to block the activity of carboxypeptidase, an enzyme which degrades enkephalins, which are morphine-like substances that can give the marathon runner what is known as a “runner’s high.” Phenylalanine also synthesizes phenylethylamine, which is the molecule found in chocolate that is responsible for pleasurable effects on mood.*

Phenylalanine is also a precursor to tyrosine, which aids in the function of the thyroid hormone production. Phenylalanine has also been shown to stimulate the release of the intestinal hormone cholesystokinin (CCK), which tells the brain when you have eaten enough food or have the sensation of fullness. Cholesystokinin helps a person feel satisfied or satiated, which can help lessen the desire for eating a second helping.*

If the supplement does not have any other ingredients....

Be who you are. Those who mind don't matter, those who matter won't mind.

The stereoisomer D-phenylalanine (DPA) can be produced by conventional organic synthesis, either as a single enantiomer or as a component of the racemic mixture. It does not participate in protein biosynthesis although it is found in proteins in small amounts - particularly aged proteins and food proteins that have been processed. The biological functions of D-amino acids remain unclear although some, such as D-phenylalanine, may have pharmacological activity.[citation needed]

DL-Phenylalanine (DLPA) is marketed as a nutritional supplement for its supposed analgesic and antidepressant activities. DL-Phenylalanine is a mixture of D-Phenylalanine and L-Phenylalanine. The reputed analgesic activity of DL-phenylalanine may be explained by the possible blockage by D-phenylalanine of enkephalin (endorphin) degradation by the enzyme carboxypeptidase A.[6] The mechanism of DL-phenylalanine's supposed antidepressant activity may be accounted for by the precursor role of L-phenylalanine in the synthesis of the neurotransmitters norepinephrine and dopamine. Elevated brain levels of norepinephrine and dopamine are thought to have an antidepressant effect. Also, as DL-phenylalanine inhibits endorphin degradation, this leads to an inhibition of GABA release in the ventral tegmental neurons (in the midbrain), which results in greater dopamine release. This can explain the analgesic effects following ingestion, D-Phenylalanine is absorbed from the small intestine and transported to the liver via the portal circulation. A small amount of D-phenylalanine appears to be converted to L-phenylalanine. D-Phenylalanine is distributed to the various tissues of the body via the systemic circulation. It appears to cross the blood-brain barrier less efficiently than L-phenylalanine, and so a small amount of an ingested dose of D-phenylalanine is excreted in the urine without penetrating the central nervous system.